We are studying the structure of the barley yellow dwarf (BYDV) virus. This virus infects and is limited to the phloem tissues of grasses. The viruses are obligately transmitted by aphids in a strain-specific and persistent-circulative manner. Virus particles contain two proteins, a major 22 kDa protein and smaller amounts of a 72kDa protein. The 72kDa protein is produced by read through of the termination codon of the gene encoding the 22kDa protein. The read-through domain has recently been shown to be present on the surface of virus particles where it may form projections which could interact with membrane bound receptors in the aphid vectors. We p!an to use the cryo-HRSEM techniques that were developed at the IMR for the study of the reo virus.